The chart shown in FIG. 1 illustrates a particularly important portion of the electromagnetic spectrum, from the point of view of technological utility. At the low-frequency (long wavelength) end of the spectrum are radio and microwaves and at the high-frequency end (short wavelength) are infra-red and visible light waves. Technological advancement based on the exploitation of both the low and high-frequency ranges of the electromagnetic spectrum has, to date, been widespread. For example, much of the presently existing wireless communication infrastructure is composed of electronic devices used to generate and modulate carrier waves in the radio/microwave portions of the spectrum. Following closely on the heels of developments in radio/microwave technology were developments in photonics and optical communications technology, which soon led to high-speed devices that employ much higher frequency carrier waves in the optical (infrared and visible) portions of the spectrum.
The region of the electromagnetic spectrum that connects the relatively low frequency microwaves to the relatively high frequency optical waves, the so-called terahertz regime, has been the latest to develop technologically, mainly due to the challenge of creating systems that may reliably generate and detect terahertz radiation. Nevertheless, the terahertz spectrum remains important for many reasons. For example, illicit drugs, explosives, and foam insulation defects all possess characteristic spectral responses in the terahertz range. In addition, the collective modes of soft condensed matter systems fall in the terahertz range, as do many molecular rotational and ro-vibrational modes. Thus, terahertz systems may be employed for trace gas sensing, food examination, package inspection, quality control, and medical imaging.
Advances in technology and applications continuously drive the demand for novel terahertz devices. For example, as communication systems press for more and more bandwidth to be used for high-speed data transmission, the demand for devices that can generate, detect, and manipulate terahertz radiation also increases. Furthermore, non-invasive and/or low health risk imaging techniques for the medical and security fields are always of great interest. To accomplish these ends, new devices that can directly manipulate terahertz radiation are needed as the foundational components of any technology that seeks to exploit electromagnetic radiation in the terahertz regime.